The present invention relates to a method and a device for controlling at least one operating-dynamics variable of a closed loop.
A system for the closed-loop control of the operating dynamics of a vehicle is described in the xe2x80x9cFDRxe2x80x94Fahrdynamikregelung von Boschxe2x80x9d, Automobiltechnische Zeitschrift, Vol. 96, No. 11, Pages 674-689 (1994). In this system, a setpoint value for the float angle and the yaw rate, respectively, are determined in each case based at least on the steering-wheel angle and the vehicular speed. The setpoint values for the float angle and the yaw rate are supplied, together with the corresponding actual values, to a state controller which ascertains setpoint vehicular yawing moments from the corresponding system deviations. These setpoint vehicular yawing moments are converted into setpoint slippage changes at suitable wheels, taking into consideration the prevailing slippage values. The setpoint slippage changes are implemented by the secondary traction control system (ASR) or anti-lock braking system (ABS) wheel controllers. No provision is made in this system for carrying out an escape turn, during which one or two rear wheels are caused to lock by actuating the parking brake.
The European Patent 0 394 387 B1 (corresponding to the U.S. Pat. No. 5,255,194) describes an anti-lock control system which includes skid detection. If it is determined that the vehicle is skidding, then the front wheels are brought into high slippage by braking, especially to the point of locking. Alternatively, provision is made for shutting down the anti-lock braking system at least partially when skidding is detected.
The object of the present invention is to improve systems for the closed-loop control of the operating dynamics of a vehicle to the effect that it is also possible to execute an escape turn with vehicles equipped with such systems.
Systems for controlling the operating dynamics of a vehicle in closed loop, hereinafter called operating-dynamics control systems, as are described, for example, in the publication xe2x80x9cFDRxe2x80x94die Fahrdynamikregelung von Boschxe2x80x9d mentioned above, seek to maintain a stable vehicle behavior under all conditions. This means that the longitudinal axis of the vehicle agrees approximately with the moving direction of the vehicle. The deviation between the longitudinal axis of the vehicle and the moving direction of the vehicle is characterized by the float angle. The float angle should not become greater than approximately 5 to 10xc2x0, since otherwise the driving condition is defined as xe2x80x9cstrongly oversteeredxe2x80x9d, which can then quickly change into xe2x80x9cskiddingxe2x80x9d. An objective of operating-dynamics control systems is to prevent this skidding. To that end, using braking interventions at suitable wheels, a yawing moment is applied to the vehicle in such a way that the longitudinal axis of the vehicle is turned toward the moving direction of the vehicle.
However, there are also cases in which the above-described stabilization of the vehicle is unwanted. This is primarily true for xe2x80x9cspecial protection vehiclesxe2x80x9d for persons who are at risk, and vehicles of security services. Here, the drivers must be able to turn the vehicle quickly by 180xc2x0 during travel. Such a driving maneuver is described as an escape turn. During the escape turn, one or two rear wheels are caused to lock by actuating the parking brake, after a yaw movement was initiated by suitable steering movements. As a result of the locking rear wheels, the lateral force to stop the yawing is lacking at the rear axle, and the vehicle turns.
At this point, an operating-dynamics control system will sharply brake a front wheel in order to reduce the lateral force at the front axle as well. In such a case, the vehicle moves laterally, but does not turn sufficiently.
In order to permit a 180xc2x0 turn triggered with the aid of the parking brake, even in the case of vehicles which are equipped with an operating-dynamics control system, this situation must be detected and the stabilizing braking interventions at the front axle or another stabilizing intervention by the operating-dynamics control system must be temporarily prevented.
To this end, the device of the present invention for controlling at least one operating-dynamics variable of a vehicle in closed loop advantageously includes arrangements that are used to ascertain whether an actuation of the vehicle parking brake, which acts particularly on the rear wheels, exists above a predefined value for the vehicular speed.
The device of the present invention also contains an arrangement by which trigger signals and/or trigger variables are ascertained at least as a function of the operating-dynamics variable. Arrangements for implementing braking interventions and/or engine interventions along the lines of a closed-loop control of the at least one operating-dynamics variable are triggered by these trigger signals and/or trigger variables. If an actuation of the parking brake exists above the predefined value for the vehicular speed, then advantageously no braking interventions and/or engine interventions, to be carried out along the lines of the closed-loop control of the at least one operating-dynamics variable, are performed.
Two procedures advantageously present themselves for this. If an actuation, according to the invention, of the parking brake exists, then either no trigger signals and/or trigger variables are ascertained, or predefined values, in particular the value zero, are output for the trigger signals and/or trigger variables.
It is particularly advantageous if, for the case when an actuation of the parking brake according to the invention exists, the braking interventions and/or the engine interventions, which are to be carried out along the lines of a closed-loop control of the at least one operating-dynamics variable, are made inoperative and/or are suppressed at least for the front wheels of the vehicle. Because of this, the device for controlling at least one operating-dynamics variable of the vehicle in closed loop is unable to reduce the lateral force at the front wheels, and thus the execution of an escape turn is first made possible.
To determine whether an actuation of the parking brake according to the invention exists, the device of the present invention first of all advantageously includes arrangements which are used to ascertain first wheel variables, and secondly includes arrangements which are used to ascertain second wheel variables. Since the intention is to make this ascertainment without additional sensors, such variables are advantageously used as first or second wheel variables which already exist in conjunction with the closed-loop control of the at least one operating-dynamics variable of the vehicle. To this end, wheel-speed variables which describe the speeds of the wheels are ascertained as first wheel variables. Pressure variables which describe the brake pressures prevailing in the wheel-brake cylinders of the wheels are ascertained as second wheel variables. The actuation of the parking brake is determined in particular as a function of the first and/or second wheel variables of the wheels upon which the parking brake acts.
The wheel-speed variables are ascertained at least as a function of wheel rotational-frequency variables detected with the aid of wheel rotational-frequency sensors. Two procedures present themselves for ascertaining the pressure variables. First of all, the pressure variables are advantageously ascertained using a mathematical model. In this case, the pressure variables are a function at least of an initial-pressure variable, which describes the initial pressure set by the driver and is detected preferably with the aid of a pressure sensor, and of the trigger signals and/or trigger variables for the arrangement for carrying out braking interventions. This procedure has the advantage that sensors can be used which already exist in the device for controlling at least one operating-dynamics variable of the vehicle in closed loop. The alternative is to detect the pressure variables with the aid of pressure sensors allocated to the wheels.
In order, as already mentioned above, to be able to dispense with a switch which indicates an actuation of the parking brake, the actuation of the parking brake according to the invention is advantageously ascertained as follows: An actuation of the parking brake exists when for at least one of the wheels upon which the parking brake acts, the corresponding first wheel variable is less than a first characteristic value, and when the corresponding second wheel variable is less than a second characteristic value. This procedure offers itself for the reason that an actuation of the parking brake becomes noticeable because the wheels upon which the parking brake acts are braked, i.e., exhibit a lower speed compared to the vehicular speed, although no brake pressure exists in the wheel-brake cylinders of these wheels.
The following further procedure is an alternative for determining whether an actuation of the parking brake exists: An actuation of the parking brake exists when for at least one of the wheels upon which the parking brake acts, the change of the corresponding first wheel variable over time is greater than a third characteristic value, and when the corresponding second wheel variable is less than the second characteristic value.
To summarize, it can be maintained that an actuation of the parking brake exists when, based on the wheel-speed variables and the pressure variables, it is determined that the corresponding speeds of the wheels upon which the parking brake acts are reducing, although these wheels are nearly brakeless.
Alternatively to the procedure indicated at the outset, in which no braking interventions and/or engine interventions are carried out in response to the existence of an actuation of the parking brake, offering itself advantageously is that the trigger signals and/or trigger variables underlying the braking interventions and/or engine interventions are ascertained as a function of a variable which characterizes the actuation of the parking brake.
Further advantages and advantageous refinements can be gathered from the subclaims, the drawing, and the description of the exemplary embodiment.